How about this #Interrail challenge: Using only Interrail, and one pass (thus max 3 months of time), and only trains, travel to stations at the edge of the accessible railway network so that the convex hull of the stations is maximally large. (I wouldn't bother trying to minimise the time taken, but that could be a separate task, to also do it as quickly as possible. The main criteria for comparing two trips is the area, though.) To make the task a bit easier, restrict it to trips that can be done without mandatory reservations. Thus leaving the UK, much of the Iberian peninsula, and Turkey out. Likely also Bulgaria and Romania. (But then most night trains are also out, and long regional train journeys will be slow. Ireland is out because you need a ferry. Sicily is out because only IC trains go on the train ferries.) To calculate the area, use the WGS-84 ellipsoid. Use the gepgrahiclib Python library.